In a high performance liquid chromatography (HPLC) system, a fluid has to be provided usually at controlled flow rates (e.g. in the range of microliters to milliliters per minute) and at high pressure (e.g. 100-2000 bar and even beyond).
The fluid, also being referred to as mobile phase, may be pumped by a high pressure pump towards a separation device. Initiated by the high pressure pump, system pressure gradually drops down to atmospheric pressure passing the chain of hydraulic communicating elements (e.g. fluid valves, sample loops, and capillary fluid connections) involved. The predominant pressure drop is expected to be at the separation device, or, in other words, the separation device forms the predominant fluid resistance within the system.
The separation device comprises a material, also being referred to as stationary phase, capable of separating different compounds of a sample being introduced into the mobile phase. Such material, usually so-called beads, which may comprise silica gel, may be filled into a column tube of the separation device that might be coupled to further elements (e.g. a detector and a fraction collector).
A liquid chromatography pumping system is described in EP 0309596 B1 by the same applicant, Agilent Technologies, depicting a pumping apparatus for delivering liquid or fluid at high pressure.
WO/2006/083776 discloses reducing pressure and flow rate variations associated with an actuation of a sample injection valve in liquid chromatography. The sample injection valve comprises a channel having a sufficient length to maintain a continuous flow path from the pump to the column during valve transition.
U.S. Pat. No. 4,506,558 discloses an injection valve for injecting a sample into a chromatography system. The valve comprises two rotor channels proving switchable liquid connections between a pump and a column, and an injection needle and a vent respectively. In addition to the ports connecting the pump, the column, the injection needle and the vent, the stator comprises a channel with interface openings, wherein the interface openings and the rotor channels are arranged such that the pump port is connected to both rotor channels during valve transition. Therewith, an interruption in flow during valve transition is avoided without providing dead space zones or blind volumes, in which a fluid does not flow with the stream.
JP 1996159310 discloses a bidirectional shear valve with a stator having a center through hole and a right and a left through hole with openings along a circle, and a rotor having an arc-line channel having a length for covering simultaneously neighboring two of said openings. Further, bypass channels are associated with two of the through holes so that a fluid communication between the center through hole and either one of the left and right through hole is maintained when rotating the rotor.
EP0022654 discloses a two-valve injection arrangement comprising two sample injection paths, allowing a simultaneous injection of a first sample and a pumping of the mobile phase comprising a second sample towards the stationary phase.